In recent years, intelligent transport systems (ITS) have been developed. One type of ITSs includes wireless base stations (roadside devices) installed in or on traffic lights for roadside-vehicle communication wherein information, such as traffic light information at an intersection (e.g., whether the light is red or green) or whether there is any vehicle turning to the right is sent to a terminal (on-vehicle device) mounted on a vehicle that is a few meters from that intersection.
On the other hand, in recent years, as middle-range high-channel-capacity wireless communication systems, standardization and development of wireless communication systems using the Orthogonal Frequency Domain Multiple Access (OFDMA) scheme which can execute flexible multiplexing into a wireless frame in the frequency domain direction and the time domain direction, namely the Worldwide interoperability for Microwave Access (WiMAX), have been carried out by the IEEE 802.16 Working Group (WG). Note that the IEEE 802.16 WG stipulates two standards: IEEE 802.16d mainly for fixed communication applications (for example, see Non-Patent References 1 and 2 which will be listed below) and IEEE 802.16e for mobile communication applications (or example, see Non-Patent Reference 3 which will be listed below).
The IEEE 802.16d and IEEE 802.16e stipulate communication between a wireless terminal (MS: mobile station) and a wireless base station (BS) wherein the MS carries out communication with the BS according to MAP information contained in a wireless frame sent from the wireless base station. A single frame of a wireless frame compliant with the IEEE 802.16e standard (WiMAX standard) (OFDMA frames) is constructed by time multiplexing a downlink (DL) subframe from the BS to the MS, and an uplink (UL) subframe from the MS to the BS.
A preamble, a frame control header (FCH), downlink MAP information (DL_MAP), uplink MAP information (UL_MAP), and one or more DL bursts (DL bursts) are multiplexed into a downlink subframe, in the two-dimensional area defined by the time domain (symbol time) direction and the frequency (subchannel frequency) direction, and one or more UL bursts (UL bursts) are multiplexed into an uplink subframe.
Here, the preamble is a domain (field) into which frame synchronous information is inserted, and the FCH is the domain in which information on the modulation scheme (e.g., QPSK, 16QAM, 64QAM), the rate code, or the like of bursts (burst profile) is inserted. Furthermore, the MAP information includes information on the identification of communication connection (CID) that is transmitted in the wireless resource used by the MS for communication, i.e., communication domain (i.e., bursts) defined by frequency (subchannel frequency) and time (symbol time (transmission timing)), the location of the burst in the wireless frame for that connection (burst location), the size of the burst (burst size), or the like.
In other words, the MAP information is defined as information (burst allocation information) that specifies (allocates) a wireless frame to be received/sent (reception domain and transmission domain) by the MS. Note that the burst location may be specified by the symbol offset and the subchannel offset from the first symbol in the wireless frame, and the burst size may be specified by the number of symbols and the number of subchannels.
Accordingly, an MS can establish wireless frame synchronization for downlink and uplink by detecting a preamble, and can selectively receive a DL burst specified in the DL_MAP which is directed to the MS by executing demodulation and decode processing on the DL burst using the encode scheme specified in the FCH, and the decode scheme corresponding to the rate code, the decode rate or the like, as well as being able to send date to a BS in a UL burst specified in the UL_MAP.
Note that other existing wireless communication schemes include techniques disclosed in Patent References 1-4 listed below.
The technique of Patent Reference 1 is directed to providing a wireless communication apparatus and an adhoc system that can improve the communication efficiency in the adhoc network and increase the network capacity and transmission speed of the network as a whole. For that purpose, in the technique of Patent Reference 1, setting information (spread codes or time slots) required for communication is provided from a master to slaves by exchanging control signals between them, and transmission/reception of data signals are directly carried out on nodes (slave-slave, and slave-master) based on the setting information within the adhoc network.
The technique of Patent Reference 2 is directed to providing a communication system and a wireless communication apparatus that can realize a seamless integration of a mobile communication network, an adhoc network, and the IP network, thereby increasing the efficiency of the usage and cost efficiency of the networks. For that purpose, in the technique of Patent Reference 2, the TDD-CDMA scheme is used as the communication scheme for both the adhoc network and the mobile communication network to use the same frequency band for the networks, thereby avoiding the complexity of the apparatuses and cost increase while facilitating switching between the networks to be connected.
The technique of Patent Reference 3 is directed to providing a media access control method and a program that enables a subscriber station (SS) outside of a communication area of a wireless base station (BS) to communicate with the wireless base station via a relay station (RS) within the communication area. For that purpose, in the technique of Patent Reference 3, a multicasted polling packet is sent by the relay station, and a wireless base station that receives the packet and the subscriber station that can directly communicate with the wireless base station operate not to receive any data packets during a predetermined time period. At the same time, subscriber stations that belong to the relay station that sends the polling packet (subscriber stations that are located outside the communication area of the wireless base station) transit to contention period with the relay station to operate to send data packets.
The technique of Patent Reference 4 is directed to allocating safety channels to terminals in a broadband wireless access (BWA) communication system. For that purpose, a method of allocating safe channels which can minimize adjacent cell interference signals with terminals located in a border area with adjacent cells in the OFDMA system, and ensuring that handover operations between the safe channels depending on channel conditions, thereby ensuring communication qualities in terminals located in the border area with adjacent cells.    Patent Reference 1: Japanese Laid-open Patent Publication No. 2005-65102    Patent Reference 2: Japanese Laid-open Patent Publication No. 2005-341290    Patent Reference 3: Japanese Laid-open Patent Publication No. 2006-196985    Patent Reference 4: Japanese Laid-open Patent Publication No. 2006-5946    Non-Patent Reference 1: IEEE 802.16-2004    Non-Patent Reference 2: IEEE 802.16-2004/Cor1/D5    Non-Patent Reference 3: IEEE 802.16e/D12